Add support for --excluded_names option

This pull request is tightly related to this pull request: https://github.com/sebastianbergmann/finder-facade/pull/4. 

This change adds support for --excluded_names option in phpcpd. This allows to filter out files, basing on pattern(s) provided by user. Most logic is implemented on library level, so this change is minor. 

Motivation for this change is described at related pull request